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InfraSonics Network: IS Net

The Infrasonics Network is a prototype system to assess the possibility
of improving warnings of severe weather events. Based upon a decade
of study at ETL, IS Net was deployed in the summer of 2003 to evaluate
it's capability to provide advance warning of tornadoes.

Results leading to the decision to construct the demonstration network

A 1995 observation of infrasound from an infrasonic observatory
co-located with the CHILL Doppler radar in NE Colorado documented
infrasound originating from the vicinity of rotation aloft, descending
to the surface in the area of a tornado report. This observation led
to a review of archived data, identifying over 100 cases where the
directions and times of signals matched documented observations of
tornadoes. Subsequent field measurements through the summer of
2002 continued to indicate that infrasound could be useful for
severe weather warning.

Potential Warning Times Estimated from Case Studies

Vortex Downward Advection

30 Minutes

Continuous Vortex 1

0 to 1 Hour 25 Minutes

Cyclic Tornado Production

1 to 3 Hours

Vortex Downward Stretching

10 Minutes

Boundary Layer Vortex Tilting and/or Stretching

Possibly 1-hour by detecting widespread processes leading to formation of landspouts

Fields of Funnels

0 to continuous monitoring

Where is IS Net being tested?

The array makes use of one existing infrasonic array at the Boulder
Atmospheric Observatory, east of Boulder, Colorado. Two additional sites
were installed near NWS radar sites in Goodland, Kansas and
Pueblo, Colorado.

A map of the prototype network with the simulation indicated by red arrows
of a triangulation on an infrasonic source in east central Colorado.

Figure of infrasonic data overlayed on WSR-88D radar image.

This is an example of a display showing actual infrasonic data overlaid
on a WSR-88D National Weather Service Doppler radar image for Denver,
Colorado. The lines are the county boundaries and the radii of the
gray circles centered on the locations of the three infrasonic
observatories indicate signal limiting noise level thresholds. Diamond
markers indicate infrasonic data points. The directions of the data
points extending outward from the gray circles indicate the directions
from which sound is arriving. The distance outward from the gray
circles indicates a measure of signal quality. Diamond data points
colored gray, indicate data between 40 and 50 on a scale of 100.
Diamonds colored yellow are data between 50 and 60. Diamonds colored
red indicate data above 60 are excellent quality signals.

This case in late October 2003 shows strong infrasound coming from
the west-north-west, probably being generated by strong winds interacting
with the mountains of central Colrorado. Such signals are not observed
during the late spring and summer months. The smaller, more continuous
data points (green to red) are the weather radar data. The color bar
at the left shows the strength of the radar reflectivity in DBZ.

In this case, the radar scan at 0.5 degrees elevation angle shows no
probable source of the strong infrasound. However, in other cases the
weather radar often detects strong echoes in the directions from which
infrasound arrives.